The present invention relates to a lock-out for a power assisted strapping tool. More particularly, the present invention relates to a lock-out for a pneumatically (or other assisted) strapping tool that prevents inadvertent out of sequence operation of the tool.
Strapping tools are well-known in the art. A wide variety of tools are known, from fully manually operated tools to automatic, table-top tools. The tools are typically designed for use with either metal strapping or plastic/polymeric type strapping.
Strappers for applying metal strapping materials are often hand-held devices. These can be fully manual, as when an operator applies a force to tension the strap and applies a force to seal the strap (either by a seal-less type of arrangement or by applying a crimp seal). Other strappers are electric or pneumatically actuated to assist in applying the force needed to tension and seal the strap.
In one pneumatic tool, tension and sealing subsystems function to separately and independently tension the strap and form a seal in the strap. The tensioning function is accomplished by actuation/rotation of a tensioning wheel that is pneumatically driven by a pneumatic motor. The strap is tensioned after a free end of the strap is secured (held) by a gripper in the strapper.
After the strap is tensioned, a sealer, also pneumatically actuated and driven, forms a seal in the strap by cutting portions of the overlapped strap layers to form interlocking members.
The tensioning function and sealing function are initiated by levers or switches on the body of the strapper. Ergonomically, in order to facilitate operation of the strapper, the switches are side-by-side. In this manner the operator can hold (support) the strapper with one hand while initiating the tensioning cycle with the other hand, and upon completion of the tensioning cycle, the operator can continue supporting the strapper and initiate the sealing cycle using the same hand that was used to initiate the tensioning cycle. Essentially, one hand is used to support the strapper and the other to operate it. In such a design, the switches for operating the strapper are next to each other so that the operator can easily support and operate the strapper from the beginning of the strapping cycle to the end of the cycle.
It has, however, been found that actuation of the sealing cycle during the tensioning cycle results in misfeeds, bad seals, and other unacceptable conditions. One such condition, referred to as ribboning, occurs when a seal is formed or partially formed in the strap prior to or while tensioning is occurring. In such a condition, the strap “ribbons” up to the sealed strap, within the looped portion of the strap.
Actuation of the sealing cycle during the tensioning cycle is generally inadvertent and is a result of bumping the sealer lever due to the close proximity of the tensioning and sealer switches, or due to improper operation. However, as set forth above, close proximity of the switches facilitates operation of the strapper. In addition, in that the pneumatic systems that are actuated by the switches share portions of the tool's pneumatic circuit, proximity of the switches permits a more compact and efficient tool design.
In an effort to prevent inadvertent actuation of the switches (in other words, inadvertently depressing the switches), while maintaining close proximity of the switches to one another, physical barriers have been positioned between the switches. Even with such barriers, it has been found that inadvertent switch actuation occurs. Moreover, it is thought to be undesirable to place a physically large barrier or separator between the switches.
Other modifications were made to the tool to prevent inadvertent actuation of the sealer cycle during tensioning, including changes to the pneumatic circuit (a delay in the sealer circuit) and increasing the force needed to depress the sealer switch. While these changes in fact did reduce the occurrence of inadvertent actuation, it nevertheless continues to occur.
Accordingly, there is a need for an interlock or lock-out for use in such a pneumatic strapper. Desirably, such a lock-out prevents inadvertent switch depression, without requiring any additional steps in operating the a strapper. More desirably, such a lock-out system adds little to no weight or large structural members to the strapper. Most desirably, such a lock-out is of the type that can be readily adapted to or retrofitted to strappers presently in use.